The applicant in patent FR 2 912 893 already proposed an electrophysiological analysis system comprising a series of electrodes intended to be positioned in different regions of the body of a patient, a DC voltage source, adapted for generating adjustable DC voltage square wave pulses, and a switching circuit, laid out for selectively connecting a pair of so-called active electrodes to the voltage source, said active electrodes making up an anode and a cathode, and for connecting at least one other electrode in high impedance. The voltage applied by the voltage source on the electrodes gives the possibility of generating in the external layer of the skin, an electrophysiological current, for which the study of certain characteristics may indicate certain pathologies. Thus for example, a low slope of the voltage-current curve may be an indication, in a diabetic patient, of diabetic neuropathy, as described in document “Gin H, et al., Non-invasive and quantitative assessment of sudomotor function for peripheral diabetic neuropathy evaluation, Diabetes Metab (2011), doi:10.1016/j.diabet.2011.05.003W.
In order to allow proper interpretation of the measurements acquired by means of this system, the quality and the relevance of this measurement has to be ensured. Therefore, it is necessary to ensure on the one hand that the model used for relating the measurements to the actual behavior of the body is reliable and relevant. On the other hand, measurements as accurate as possible have to be conducted, by limiting at most the uncertainties and the biases related to the measurement system.
Now the voltammogram (i.e. the voltage-current curve of the response of a dipole) of an electrode, typically in nickel or stainless steel, used as an anode or cathode, was studied in solutions mimicking sweat, which is illustrated in FIG. 1. In a way known per se, oxidation and reduction reactions respectively at the anode and at the cathode are encountered, related to the application of a potential on these electrodes. On the anode side, chlorides participate in the oxidation of the anode and a wall is formed beyond a certain voltage threshold. On the cathode side, a reduction of possible oxides and reduction of the water present in the sweat are encountered, causing evolvement of hydrogen. The cathode is then reduced, which also leads to the formation of a wall below a voltage threshold.
The position of these oxidation and reduction walls on the voltammogram depends on the electrode (composition, rate of use) as well as on concentrations of electrolytes causing oxidation-reduction reactions. The voltammogram thus represents the intrinsic behavior of the electrode, i.e. the maximum current which it may transmit for a given potential, and which is governed by the charge transfer between the electrode and the electrolyte. It is understood that oxidation of the anode involves gradual generation of an overvoltage which biases the measurements. It is therefore necessary to obtain more accurate measurements than those obtained up to now with the system described hereinbefore, in particular by correcting the measurement biases related to the electrodes.